In general, the invention relates to land grid arrays (LGA), and more specifically, the invention relates to installation of LGA multi-chip modules.
Area array socket connectors are an evolving technology in which an electrical interconnection between mating surfaces is provided through a conductive interposer. One significant application of this technology is the socketing of land grid array (LGA) modules directly to a printed wiring board in which the electrical connection is achieved by aligning the contact array of the two mating surfaces and the interposer then mechanically compressing the interposer. LGA socket assemblies are prevalent today in the electronics industry, but they are typically used to attach single-chip-modules to printed wiring boards. The demand for higher performance is driving the requirement to develop LGA socket assemblies for multi-chip modules.
One of the problems confronting the design of multi-chip module socket assemblies is developing a mechanical system to generate the large force required to compress the increased contact area of the interposer without interfering with the heat transfer system of the module, distorting the printed wiring board, or occupying a significant portion of the volume of the enclosure in which the module is housed. A system has been devised to solve this problem utilizing one or more load posts attached to the module. The load posts pass though the printed wiring board and a mechanical system incorporating a stiffening plate to reduce printed wiring board distortion is then employed to exert a large tensile force on the load posts pulling the module toward the printed wiring board and compressing the interposer. Since the mechanical system used to compress the interposer is on the side of the printed wiring board opposite the module, it may not occupy any volume of the enclosure nor interfere with heat transfer. One drawback of this system is that if the printed wiring board is mounted vertically, it is very difficult for one person to actuate the connection system on the opposite side of the printed wiring board while holding the multi-chip module in place.
The surface of the module that contacts the printed wiring board has a plurality of electrical connection points attached to circuits within the module. The electrical connection points on the module need to be aligned with corresponding electrical connection points on the printed wiring board to yield the desired operation of the circuits. If the module is symmetrical, it may be inserted into the socket in more than one orientation. Insertion of the module into the socket in an orientation other than that intended may result in the electrical connection points not being properly aligned. A keying mechanism may be employed to change the geometry of the module and socket to an asymmetrical shape so that the module can only be inserted into the socket in one orientation.
The demand for higher performance is also driving the density of components mounted to the printed wiring board to increase, reducing the visibility of the technician to guide the module into the socket. Contacting the module to surrounding electrical components may damage the module, the LGA interposer, or the contacted component. The addition of guiding members on the socket may aid the technician in inserting the module into the socket reducing the risk of potential damage.
The module may include electrical circuits employing low break down voltage, high impedance, semiconductor devices. If an electro-static charge is allowed to accumulate near a semiconductor, the charge may increase to a level sufficient enough to ionize a path to ground through the semiconductor. The discharge of an electrostatic charge through a semiconductor may break down the semiconducting material effecting the circuit operation. Airborne dust particles blown by a fan, used to cool a heat sink attached to the module, may rub against the heat sink and other components in the air flow causing static charges to accumulate. Using electrically conductive material for the heat sink and components in the airflow and electrically connecting them to ground may aid in dissipating electro-static charges.
What is therefore needed is a method and holding member that will guide and orientate an multi-chip module into a socket, temporarily retain the module freeing the technician to move to the opposite side of the printed wiring board and actuate the mechanical connection system, and provide a ground path to dissipate any static charge accumulated on the heat sink attached to the module.
One aspect of the invention provides a method of installing a land grid array (LGA) multi-chip module to a printed wiring board. A module holding member is attached to the printed wiring board. A module assembly is inserted into the module holding member. The module assembly is retained to the module holding member. The module assembly is electrically connected to the printed wiring board while the module is retained to the module holding member. The holding member may apply a force to an outer surface of the module assembly. A cam may be rotated to apply a force to an outer surface of the module assembly. A socket site in the module holding member may position the module assembly. The module holding member may guide the module assembly. The module assembly may be keyed into the module holding member.
Another aspect of the invention provides an installation apparatus for a land grid array (LGA) multi-chip module utilizing a frame member surrounding an LGA socket site. At least one retaining member operably attached to the frame, wherein the frame is attached to a printed wiring board and a LGA multi-chip module assembly is installed onto an LGA socket site and retained to the module holding member with the retaining member. The frame member may comprise conductive plastic. The frame member may include a chamfered corner to orientate the module assembly. A retaining member may be comprised of a cam. Cam receptors may receive cam members. Cam members may be attached to the cam receptors. The cam member may include a hexagonal column. The cam member may include an inclined plane. The inclined plane may include a stop. The frame may include a guide portion. The frame member may include mounting pads. The wall of the frame may include a stiffening rib.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawing.